The present invention concerns a piston and piston ring for a hydraulic or pneumatic mechanism and especially for a dashpot.
That friction between the piston and cylinder can be decreased by mounting a preferably plastic ring around the outer surface of the piston is known.
DE 3 701 757 A1 discloses such a piston and ring. The ring is accommodated in a groove that extends around the outer surface of the piston. The ring that characterizes this particular prior art is very thin-walled and is accordingly also referred to as xe2x80x9csheetxe2x80x9d. There are drawbacks to this system due to the need to maintain precise tolerances between the dimensions of the groove, the diameter of the cylinder, and the thickness of the sheet. These tolerances must allow the piston to travel in and out of the cylinder smoothly and can lead to displacement of the ring within the groove. The resulting rumbling noise can be heard inside the vehicle.
Tensioning the ring inside the groove axially or radially is known from DE9017933U1. The tensioning means, however, are very complicated and accordingly expensive.
The object of the present invention is to combine such a generic piston with a ring in such a way as to prevent rumbling in an embodiment that will be simple to produce and include few components.
The major advantages of the present invention are that the two-part piston and its associated ring are easy to manufacture and that the ring will be reliably tensioned to the piston without being essentially dependent on the tolerances of the components. Above all, no rumbling will be perceptible from inside the vehicle.